The electronic control of the light direction of a collimated flat illuminator is a difficult technical problem and hence there have been few solutions to this.
WO 2013/180725 (Hewlett Packard) describes a lightguide that has patterned nanostructured extraction features where different colours (for example lasers in-coupled to the lightguide) can be directed, by diffraction, on a pixel basis in different directions. The result of this is at different images can be viewed by viewers from different directions. The images are fixed and it is not possible to adjust the images or the directions once the lightguide has been made.
U.S. Pat. No. 8,659,830 (3M) illustrates a sequential autostereoscopic display with switchable viewing zones. In this invention an LCD is placed on a backlight. The backlight is able to switch sequentially between two viewing directions corresponding to the two eyes of a viewer. Alternative images in sequence to this switch are shown on the LCD and the viewer sees an autostereoscopic image. The backlight achieves this by having two sets of LEDs at opposing ends of the lightguide and extraction features that extract light in opposing directions. A symmetric film, consisting of aligned prisms and lenses on opposing faces, directs the two opposing light directions in the two directions required. The LEDs are then sequentially switched on and off.
U.S. Pat. No. 7,970,246 (Microsoft) describes an alternative approach where a lightguide is made in a tapered cross section with the taper towards a point light source. The far side of the lightguide is curved so as to reflect and collimate the light emerging from the light source and is then extracted by the light passing back down the taper. The extracted light is then turned using a turning film. The taper width and shape of lens is chosen to obtain a uniform extraction. Multiple light sources along the edge will form collimations in different directions depending on its location relative to the curved surface of the far end of the lightguide. The different collimation directions thus extracted in different directions.
A similar invention is proposed in US 2012/0299913 and US 2012/0243204 (RealD) where the nature of the extraction features differs only over the Microsoft invention.